Now it's time to define what observer pattern is:
Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
This code has already shown part of the observer pattern:
- BankAccount class is the subject
- IAccountObserver is the observer
- Emailer & Mobile classes are the ConcreteObserver
The code changed compared to step 2 is highlighted in Bold:
public class BankAccount
{
ArrayList<IAccountObserver> observerList = new ArrayList<IAccountObserver>();
public void Withdraw(int data)
{
//...
UserAccountArgs args = new UserAccountArgs();
//...
foreach (IAccountObserver observer in observerList)
{
observer.Update(args);
}
}
public void AddObserver(IAccountObserver observer)
{
observerList.Add(observer);
}
public void RemoveObserver(IAccountObserver observer)
{
observerList.Remove(observer);
}
}
public interface IAccountObserver
{
void Update(UserAccountArgs args);
}
public class Emailer : IAccountObserver
{
public void Update(UserAccountArgs args)
{
//...
string toAddress = args.ToAddress;
}
}
public class Mobile : IAccountObserver
{
public void Update(UserAccountArgs args)
{
//...
string mobileNumber = args.MobileNumber;
}
}
